Effects of Structural Motion on the Aerodynamics of the X-56A Airfoil

This work presents experimental and computational results regarding the effects of structural motion on the aerodynamics of the X-56A airfoil. An oscillatory plunging mechanism has been fabricated and installed in a subsonic wind tunnel. The static characteristics of the X-56A were verified before focusing on unsteady behavior at Re=200k with nominal angles of attack of 10 and 12 degrees. The former contains a laminar separation bubble near the leading edge while the latter is nearly the angle of CLmax. Instantaneous angles of attack during the airfoil oscillations are outside the linear CL-alpha regime and extend into the region associated with static stall in most cases. Focus is placed on oscillations with dimensionless amplitude and frequency that produce CL values which are unattainable in static tests even at higher Re. A comparison with unsteady aerodynamic theory (Theodorsen) is very good for the lower angle of attack case (10 degrees), but unwarranted at the higher angle (12 degrees) since viscous effects become more prominent. The lower angle of attack case is also supported by CFD which reveals more detailed information on the laminar separation bubble near the leading edge and the turbulent flow downstream.